Devices and methods related to controlling ue assumption of interface

ABSTRACT

To control UE assumption of interference there is a controller module to control a plurality of transmission points, each constituted by a set of at least one transmit antenna, to transmit data to another device in a coordinated transmission from at least a subset of the plurality of transmission points. The controller module is configured to allocate, to each resource linked to the subset of the plurality of transmission points, an interference contribution parameter that is indicative of an expected interference contribution originating from said transmission point, and to inform said another device of those resources to which the subset of the plurality of transmission points is linked, together with the respective interference contribution parameter allocated to each resource. Another device reports feedback based on signals which are scaled with the respective interference contribution parameter.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation application which claims the benefit of priorityunder 35 U.S.C. §120 of U.S. application Ser. No. 13/292,205, filed Nov.9, 2011, which claims the benefit of priority under 35 U.S.C. §119(a)and 37 C.F.R. §1.55 of UK Patent Application 1119208.5, filed on Nov. 7,2011.

FIELD OF THE INVENTION

The present invention relates to devices, methods and computer programproducts configured to be deployed in a scenario for mobilecommunication which scenario comprises a plurality of transmissionpoints, each constituted by a set of at least one transmit antenna, fortransmitting data to another device in a coordinated transmission fromat least a subset of the plurality of transmission points. Moreparticularly, it relates to such devices, methods and computer programproducts related to controlling UE assumption of interference.

BACKGROUND

Mobile data transmission and data services are constantly makingprogress. With the increasing penetration of such services, datathroughput and transmission reliability find more and more attention.

Under one aspect, investigation is made in scenarios for mobilecommunication which comprise a plurality of transmission points, eachconstituted by a set of at least one transmit antenna, for transmittingdata to another device in a coordinated transmission from at least asubset of the plurality of transmission points.

It should be noted that concepts outlined in connection with the presentinvention are generally independent of any particular communicationstandard; rather, they are generally applicable to a variety ofcompatible standards. In order to properly describe the concept(s),however, for explanatory purposes only and without any intention tolimit the applicability of the concept(s) introduced in thespecification to a particular standard, those concept(s) are describedwith reference to an example scenario. As the example scenario, LTE(Long Term Evolution) and/or LTE-A (LTE-Advanced) was chosen for thenetwork infrastructure.

That is, e.g. in the 3rd Generation Partnership Project (3GPP) Long TermEvolution (LTE) and LTE-Advanced (LTE-A), single cell single-user (SU-)and multi-user (MU-) multiple-input multiple-output (MIMO) networkperformance is interference-limited, especially at the cell edge.

Therefore, introduction of the coordinated multipoint (CoMP)transmission/reception technology has been considered, where in downlink(from a network device such as an eNB (evolved NodeB) towards a terminalsuch as a user equipment UE), multiple points co-operate in schedulingand transmission in order to strengthen desired signal and mitigateinter-cell interference. According to e.g. the 3GPP technical report onCoMP, TR36.819, a point is defined as a set of geographically co-locatedtransmit antennas and the sectors of the same site correspond todifferent points. It should be noted that a cell is formed by one ormultiple points.

The above mentioned CoMP TR was approved after a recent RAN meeting. Theagreed CoMP working item definition proposes the following focus for theCoMP work during a subsequent release (e.g. Rel-11):

-   -   “The work for specifying CoMP support in Rel-11 should focus on    -   Joint transmission (JT)    -   Dynamic point selection (DPS), including dynamic point blanking    -   Coordinated scheduling/beamforming (CS/CB), including dynamic        point blanking”.

In joint transmission (JT) CoMP, two or more points transmitsimultaneously to a CoMP user. Dynamic point selection (DPS) on theother hand refers to a scheme where the transmission point is switchedaccording to changes in signal strength. In coordinatedbeamforming/scheduling (CB/CS), in turn, the scheduling decisions ofneighbor points are coordinated in order to reduce interference. Inprinciple, all schemes may include blanking/muting which means that oneor more transmission points are blanked/muted (switched off or not usedfor transmission) to decrease the interference.

The agreed CoMP working item targets specification of intra-cell andinter-cell DL CoMP schemes which operate in homogeneous andheterogeneous configurations. Four main scenarios have been studied sofar:

-   -   intra-site (scenario 1),    -   inter-site with high power remote radio head (RRH) (scenario 2),        low power RRH within the coverage of the macro cell, without and        with the same cell ID (scenarios 3 and 4, respectively).

CoMP working item addresses both frequency division duplex FDD and timedivision duplex TDD. Hence, unified solutions should be targeted, as itis always the case in LTE specifications.

CoMP is intended to improve the performance of cell edge users, asespecially at cell edge the performance is interference limited. A CoMPmeasurement set is formed by M cells/points for which the UE ismeasuring channel state information. The reporting set has been limitedto N cells/points defining the number of points for which CSI feedbackis reported. A common assumption has been that the CoMP reporting set isformed by two to three points. Also the CoMP reporting set could beequivalent to the CoMP measurement set. The number of points involved inCoMP scheme (cooperation set) does not need to be signaled to the UE ormentioned in specifications but is left for network implementation. Thepoint from which the UE would receive transmission in single-cell modeis defined as the serving point.

In Release 10, different reference signals (RS) were defined for CSIestimation and data demodulation purposes. Namely, channel stateinformation reference symbols (CSI-RS) and demodulation referencesymbols (DM-RS).

Such reference symbols are assigned to (specific) physical resourceelements RE within physical resource blocks PRB. A resource element REis represented by a time slot and a frequency (bandwidth) assigned to itwithin the frequency-time domain. A plurality (defined number) ofresource elements in frequency/bandwidth domain form a physical resourceblock PRB (in frequency domain), and a plurality of PRBs are presentwithin a channel.

PDSCH (Physical downlink shared channel) resource element muting is alsospecified, allowing for multi-cell channel estimation. The baselinefeedback has been agreed to be implicit feedback which consists of rankindicator (RI), precoding matrix index (PMI) and a channel qualityindicator (CQI). Hence, the UE estimates the channel, selects rank andPMI and calculates the post-processing (after receiver) SINR (signal tointerference noise ratio) and derives the CQI based on that. CQI may beseen as indicative of the post processing SINR. Release 10 feedbackoperates per point. The CoMP specific flavors are that a UE may receiveCSI-RS resources from more than one point and it is possible to designaggregated (over multiple CSI-RS resources) or per point (per CSI-RSresource) feedback. The per-point PMIs may be improved by a combinerfeedback that may be an inter-point phase and/or amplitude value.

Table 1 summarizes the feedback and channel estimation options for eachCoMP scheme.

TABLE 1 Feedback for different CoMP schemes JT DPS + muting CS/CB +muting Feedback 1) Per point Per point PMI/ Per point PMI/CQI PMI/CQICQI + point or CS/CB + muting (+combiner) selection + specificadditional 2) Per point PMI possible feedback (+combiner) + mutingaggregated CQI + indication serving point CQI 3) Aggregated PMI/CQI +serving point PMI/CQI Channel Per point CSI-RS Per point CSI- Servingpoint estimation or aggregated single RS CSI-RS + possibly CSI-RSpattern other point CSI-RS

During a recent RAN meeting, the following working assumption wasagreed:

“Definition: “CSI-RS resource” here refers to a combination of“resourceConfig” and “subframeConfig” which are configured by higherlayers.

Standardize a common feedback/signaling framework suitable for scenarios1-4 that can support CoMP JT, DPS and CS/CB. Feedback scheme to becomposed from one or more of the following, including at least one ofthe first 3 sub-bullets:

-   -   feedback aggregated across multiple CSI-RS resources    -   per-CSI-RS-resource feedback with inter-CSI-RS-resource feedback    -   per-CSI-RS-resource feedback    -   per cell Rel-8 CRS-based feedback    -   Note that use of SRS sounding reference signal (SRS) used in        uplink measurement may be taken into account when reaching        further agreements on the above.”

The CoMP problem relates mostly to the CQI feedback. The CQI is used bythe eNB to perform adaptive modulation and coding which means thetransmission rate is adapted based on channel conditions. Accuracy ofthe CQI value affects greatly on the system performance, especially ifthe CQI is overestimated and too high transmission rate is assignedwhich is not supported by the actual radio link. The CQI depends on thetransmission hypotheses made by UE at a given time. For example:

-   -   When reporting an aggregated JT CQI, UE assumes combined        transmission from N points to the UE,    -   When reporting a DPS CQI without muting, UE assumes transmission        from a selected transmission point and interference from other        transmission points,    -   When reporting a DPS CQI with muting, UE assumes transmission        from one point and zero interference from points that are        assumed to be muted,    -   When reporting CQI for CS/CB, UE assumes transmission from one        point and reduced interference or muting from other transmission        points.

In addition to the transmission hypothesis, the CQI value depends on thehypothesis of the interference. The exact interference level depends onthe exact scheduling decisions and used PMIs in the other cells at timeof transmission. It follows that the level of the exact interference isnot known at the UE at the time when CQI is evaluated. The UE is notaware of a scheduling decision of any eNB without signaling, andmoreover, the scheduling decisions affecting the experiencedinterference level are not yet even made, and thus cannot be signaledeven if that kind of signaling would be possible. For the case of CS/CB,the coordination between points reduces the level of interference butthe level of interference reduction is typically not known by the UE.

In a recent RANI meeting, several companies contributed aspects relatedto CoMP CQI. Out of these, one did not discuss the CQI derivationdetails. Others presented equations on how the eNB can derive the CQIfor joint transmission from per point CQIs with a given assumption oninterference. The assumptions on how the UE would estimate theinterference level for the per-point CQIs was not considered.

A further contribution discusses measurement objectives as follows“Observation 1: for each CoMP scheme, considering the coordinationmethod, the interference should “Include signals from all thepoints/cells outside of the transmission set or coordination set,Consider the actual resource elements causing interference to the PDSCH,Not include signals from the point/cell the UE assumes as transmittingthe PDSCH, Not include signals from the point/cell with blanking on someor all resource elements”.

But no concrete scheme for implementation is discussed/presented.

A more related prior art addressing estimation of interference level forderiving a CQI can be found in a previous standard. The energy perresource element (EPRE) is assumed to be different for the CSI-RS fromwhich the channel is estimated and for the PDSCH where the data istransmitted. As stated in TS36.213, V.10.3.0, section 7.2.5, a parameterP_c is defined that indicates the ratio between PDSCH EPRE and CSI-RSEPRE and it is signaled to the UE. The parameter is referenced asp-C-r10 in TS36.331 v.10.3.0 in section 6.3.2. This parameter is part ofthe PhysicalConfigDedicated information element used to specify the UEspecific physical channel configuration on a transmission carrier. Thisparameter is needed for the CQI derivation in current system, and theparameter is user and transmission frequency specific.

Assuming that UE estimates signal power from the CSI-RS, P₀, and othercell interference and noise power N, the final CQI is based on theSINR=P_c P₀/N. Thus the current definition of P_c is applied to the“useful” (payload) signal transmission to the UE.

Thus, existing and/or discussed systems for CoMP still lack fullyappropriate feedback from terminals so as to properly estimate/take intoaccount also interference experienced by the terminals.

Thus, there is still a need to further improve such systems.

SUMMARY

Various aspects of examples of the invention are set out in the claims.

According to a first aspect of the present invention, there is provided

-   -   a device, comprising a controller module, configured to control        a plurality of transmission points, each constituted by a set of        at least one transmit antenna, to transmit data to another        device in a coordinated transmission from at least a subset of        the plurality of transmission points, wherein the controller        module is configured to allocate, to each resource linked to the        subset of the plurality of transmission points designated for        transmission towards the another device, an interference        contribution parameter that is indicative of an expected        interference contribution originating from said transmission        point, and to inform said another device of those resources to        which the subset of the plurality of transmission points        designated for transmission towards the another device is        linked, together with the respective interference contribution        parameter allocated to each resource, as well as    -   a device, comprising a controller module, configured to report        feedback to another device responsive to the another device's        coordinated transmission from at least a subset of a plurality        of transmission points, each transmission point being        constituted by a set of at least one transmit antenna, wherein        the controller module is configured to receive, for each        resource to which the subset of the plurality of transmission        points designated for the another device's coordinated        transmission is linked, a respective interference contribution        parameter allocated to each resource and indicative of an        expected interference contribution originating from said        respective transmission point, measure a channel transfer        function for each channel established towards the device by a        respective resource to which the subset of the plurality of        transmission points designated for the another device's        coordinated transmission is linked, measure interference        originating from resources not linked to said subset of the        plurality of transmission points, obtain a feedback signal        indicative of the channel quality for each resource linked to        the subset of the plurality of transmission points and        transmitting a payload signal, derive a feedback signal        indicative of the channel quality for each resource linked to        the subset of the plurality of transmission points and        transmitting an interfering signal, sum the derived feedback        signals scaled with the respective interference contribution        parameter allocated to the respective resource, and the measured        interference, and select a reporting signal for being fed back        to the another device based on the result of summing and the        respective channel quality. According to a second aspect of the        present invention, there is provided    -   a method, comprising controlling a plurality of transmission        points, each constituted by a set of at least one transmit        antenna, to transmit data to another device in a coordinated        transmission from at least a subset of the plurality of        transmission points, allocating, to each resource linked to the        subset of the plurality of transmission points designated for        transmission towards the another device, an interference        contribution parameter that is indicative of an expected        interference contribution originating from said transmission        point, and informing said another device of those resources to        which the subset of the plurality of transmission points        designated for transmission towards the another device is        linked, together with the respective interference contribution        parameter allocated to each resource.    -   as well as    -   a method, comprising reporting feedback to another device        responsive to the another device's coordinated transmission from        at least a subset of a plurality of transmission points, each        transmission point being constituted by a set of at least one        transmit antenna, receiving, for each resource to which the        subset of the plurality of transmission points designated for        the another device's coordinated transmission is linked, a        respective interference contribution parameter allocated to each        resource and indicative of an expected interference contribution        originating from said respective transmission point, measuring a        channel transfer function for each channel established towards        the device by a respective resource to which the subset of the        plurality of transmission points designated for the another        device's coordinated transmission is linked, measuring        interference originating from resources not linked to said        subset of the plurality of transmission points, obtaining a        feedback signal indicative of the channel quality for each        resource linked to the subset of the plurality of transmission        points and transmitting a payload signal, deriving a feedback        signal indicative of the channel quality for each resource        linked to the subset of the plurality of transmission points and        transmitting an interfering signal, summing the derived feedback        signals scaled with the respective interference contribution        parameter allocated to the respective resource, and the measured        interference, and selecting a reporting signal for being fed        back to the another device based on the result of summing and        the respective channel quality.

Advantageous further developments are as set out in respective dependentclaims.

According to a third aspect of the present invention, there are providedcomputer program products comprising respective computer-executablecomponents which, when the program is run on a computer, are configuredto perform the above method aspects, respectively.

The above computer program product may further comprisecomputer-executable components which, when the program is run on acomputer, perform the method aspects mentioned above in connection withthe method aspects.

The above computer program product/products may be embodied as acomputer-readable storage medium.

The methods, devices and computer program products described in thisdocument use, at least in exemplary embodiments, a UE based feedbacksuch as CQI in support of CoMP, wherein the feedback signals are basedon UE assumptions of interference when computing CQI. The UE is informedof those assumptions to use and those are thus controlled by a networkdevice such as an eNB.

This invention thus improves interference estimation for CoMP, and inparticular controls the UE assumption about the interference, i.e. howto make the UE to take coordination into account in CQI reporting. Underat least one aspect, this is achieved by, among other features, theintroduction of transmission antenna port or transmission point-specificparameters which are referred to herein as “interference contributionparameters” (or also named “power offset parameter”) and which areindicative of an expected interference contribution originating from arespective transmission point.

Thus, performance improvement is based on methods, devices and computerprogram products enabling such feedback to be provided contribute to animproved CQI estimation for CoMP, provide for a simple implementation ofcoordinated beamforming/scheduling-type of CoMP schemes, whilealleviating a need to consider spatial information feedback forcoordinated beamforming purposes.

With the interference contribution parameters (aka power offsetparameters), the eNB can control the UE assumption about theinterference power, which will be useful for example if the eNB is doingcoordinated beamforming or scheduling in order to reduce theinterference levels. Such an approach avoids having to rely on spatialinformation feedback (e.g. best companion PMI feedback) for coordinatedbeamforming CQI calculations.

BRIEF DESCRIPTION OF DRAWINGS

For a more complete understanding of example embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates an overview of devices/entities involved;

FIG. 2 illustrates a flow chart of a processing at a network device suchas an evolved NodeB eNB; and

FIG. 3 illustrates a flow chart of a processing at a terminal devicesuch as an user equipment UE.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary aspects of the invention will be described herein below.

Generally, the invention is implemented in a framework for a coordinatedtransmission from multiple points or antennas, as illustrated in roughoutline in FIG. 1.

FIG. 1 illustrates an overview of devices/entities involved withreference to entities known from LTE/LTE-A. Other names may be assignedto similar entities in other standards, while as long as thefunctionality imparted thereto remains the same or substantiallysimilar, the present invention s described herein below will remainapplicable also to those other standards.

As shown in FIG. 1, an eNB at site #1 comprises a control module as wellas transmitter antennas Tx12 and Tx11 defining sectors 1B and 1A,respectively, each sector representing one point (as a set of at leastone geographically co-located antenna). The eNB has (is connected to)also one (potentially also more) remote radio heads RRH at another site,site #2. The RRH at site #2 is under control of the eNB and comprisestransmitter antennas Tx21 and Tx22 defining sectors 2A and 2B,respectively, each sector representing one point. (Note that asillustrated in FIG. 1, to Tx21 and Tx22, respectively, a parameter alpha(α) is assigned; these correspond to sets of antennas, a set may beminimum one, but as LTE is MIMO based, it is possible to be two ormore.) Sectors 1A and 2B form a cooperation area/set x, while Sectors 1Band 2A form cooperation area/set y. To each point is associated aparameter alpha_11 (α_11), alpha_12 (α_12), alpha_21 (α_21), andalpha_22 (α_22). In case of only one antenna (or antenna port) beingallocated to a point, the parameter alpha of the point may be identicalto the parameter of the antenna, otherwise, it is derived from theplurality of the antenna parameters constituting the point. The eNB andRRH transmit in cooperating mode from cooperation sets in downlink DL toa terminal or user equipment UE. DL transmission from points Tx11, Tx22forming cooperation area x, and DL transmission from points Tx12 andTx21 forming cooperation area y represent a joint transmission JT modeor dynamic point selection DPS mode.

Transmission from the transmission points is performed using specificresources i.e. resource elements RE within the PRB, and thus theparameters alpha_11, alpha_12, alpha_21, alpha_22 are assigned to thoseresources which are thus linked to the transmission points.Transmissions used for measurement purposes are referred to as referencesignals RS. Thus, transmission from eNB to the UE for measurementpurposes to derive a channel state indication/information CSI areaccomplished in so-called CSI-RS reference signals in specific resourceelements RE within a PRB.

Hence, the eNB represents a device comprising a controller module,configured to control a plurality of points, each constituted by a setof at least one transmit antenna, to transmit data to another device ina coordinated transmission from at least a subset of the plurality ofpoints. The controller module is configured to allocate, to eachresource linked to the subset of the plurality of points designated fortransmission towards the another device UE, an interference contributionparameter that is indicative of an expected interference contributionoriginating from said point. This is the parameter alpha_11, alpha_12,alpha_21, alpha_22 (and/or the CSI-RS configuration parameter).

The terminal UE sends in uplink (UL) direction a signal RSRP (referencesignal received power) to the eNB, receives interference contributionparameter(s) “alpha” indicative of an expected interference contributionoriginating from a respective point, processes this parameter along withother estimated parameters, and returns a channel quality indication CQIto the eNB.

This will be detailed further herein below in various aspects involved.As outlined above, at least aspects of the invention comprise a CoMP CQImeasurement framework for support of various different CoMP schemes.

Insofar, the invention consists of at least the following two aspects:

Interference measurement:

-   -   UE measures the interference underlying the whole CoMP reporting        set, and adds (performs a summing of) interference from selected        CSI-RS resources (points) according to the assumed CoMP        transmission hypothesis;

Scaling of the interference coming from points that are part of the CoMPreporting set:

-   -   The eNB signals to the UE potentially CSI-RS resource        (point)—specific interference contribution parameter(s) “alpha”        (aka power offsets parameters). These are the parameters (power        offsets) that the UE should assume between CSI-RS and PDSCH when        estimating the interference.

The signaling for informing the UE of these parameters can be based onhigher layer signaling such as radio resource control, RRC, signaling,or alternatively a faster solution based on using the physical downlinkcontrol channel (PDCCH) could be implemented.

It is to be noted that the interference contribution parameter or poweroffset parameter as introduced in this document is different from theparameter P_c used in Release 10 for scaling CQI. Here, the (newlydefined) interference contribution parameter is used for scalingindividual components of interference rather than the overall CQI orindividual components of the payload (“useful”) signal.

Additionally, as will be discussed later, this may involve under atleast an exemplary modification, a configuration for the terminal UEwith two separate power offsets parameters (potentially per point), i.e.the interference contribution parameter alpha and the parameter P_cmentioned above.

An example of CQI computation for the case of three co-operating cellsor points will be given with following notation:

W=W(H_(0′)H_(1′)H_(2′)α_(0′)α_(1′)α_(2′) ^(N)) is the receiver filterfor a MIMO stream;

(Note that the exact receiver filter depends on the CoMP schemeassumption (transmission assumptions) and on assumptions what kind ofreceive filtering is used. A typical assumption is an MMSE type (minimummean square error) of receiver.

For such receiver type, channels from transmission points that transmitthe useful signal (payload) are aggregated into one H_(own) andtransmission points generating interference are summed in H_(int).

w=H_(own) ^(H)(H_(own)H_(own) ^(H)+H_(int)H_(int) ^(H)+R_(N))⁻¹,

where ( )^(H) is conjugate transpose and R_(N) is the noise covariance.For white noise it would be an identity matrix times the noisevariance.) H_(i) is the effective radio channel (channel transferfunction) including precoding from transmission point i;

N is the thermal noise plus, originating also from interference poweroutside of the CoMP measurement set;

(Note that N includes the thermal noise that is determined as thethermal noise level at the receiver. Thermal noise is independent of thetransmission scheme. N includes also the interference power level ofinterference coming outside the CoMP set.)

α_(i) is the power offset parameter (i.e. interference contributionparameter) signaled to UE, corresponding to transmission point i.

The final CQI feedback can be based on the signal to interference noiseratio, SINR, for example for a transmission hypothesis that onlytransmission point of index i=0 is transmitting (the payload or “useful”signal) and signals from transmission points i=1 and i=2 areinterference. Other hypotheses can be made, for example that point 1 istransmitting the payload and rest are interference etc.

The SINR is the computed as follows according to an aspect of theinvention:

${{SINR} = \frac{\alpha_{0}{WH}_{0}H_{0}^{H}W^{H}}{{WNW}^{H} + {\alpha_{1}{WH}_{1}H_{1}^{H}W^{H}} + {\alpha_{2}{WH}_{2}H_{2}^{H}W^{H}}}},$

The smaller the values of the power offset parameter, i.e. theinterference contribution parameter α_(i) are, the closer to muting theinterference assumptions are. Thus, with these interference contributionparameters α_(i), flexible configurations between full interference andmuting are possible to be indicated to the UE.

Hence, by controlling the parameters and informing them to the UE, thenetwork, i.e. eNB, can implement different CoMP schemes, e.g.:

α_(i)=0 implies that the UE will assume blanking of the transmissionfrom such transmission point linked to CSI-RS resource(s) i in CQIcalculation;

0≦α_(i)<1 implies that UE will assume reduced interference from suchtransmission point(s) linked to the CSI-RS resource(s) i in the CQIcalculation. This could be for example due to spatial coordination (e.g.CB) or coordinated scheduling (CS) (e.g. reducing transmission power forinterfering point).

Alternatively, the value can contain the scaling difference P_c betweenthe PDSCH and CSI-RS EPRE like in the prior art system.

Insofar, a parameter assigned to the point/resource carrying the payloadsignal may have two components α₀ and P_c.

Namely, if the transmission point is transmitting the desired payloadsignal, alpha does not apply. The UE can still be configured withwhatever value for alpha, but if in the CoMP transmission hypothesis UEassumes that desired signal is transmitted from the point, alpha is justnot used.

That is, interference contribution parameter a may be 1 or α may be P_cfor the serving point (transmitting the payload in assigned resources).For interfering points α may be between 0 and 1, if it does not includeP_c, or between 0 and P_c if it does include P_c. If α does include P_c,then P_c is not signalled separately but the α may be defined as anotherparameter in addition to the P_c.

Stated in other words, a first way is to have two parameters for eachpoint, namely alpha and P_c. When the corresponding point is taken as(assumed to transmit) the desired signal in the CoMP transmissionhypothesis, use is made of P_c. When it is taken as interference, use ismade of alpha for the scaling.

A second way is that alpha is used on top of P_c, i.e. it is alwaysscaled by both the interference. Then for useful signal we scale by P_c(alpha is then fixed to 1), and for interference we scale by alpha*P_c.

As mentioned, power is scaled by two factors, by P_c due to transmitpower offset and by a as an interference contribution parameter thatdescribes the reduction in interference level. The α can be defined inexemplary embodiments as scaling factor that includes both, but shouldat least include the indications of the reduction of the interferencelevel, but when scaling, in exemplary embodiments, both the interferencecontribution parameter and P_c should be taken into account.

A corresponding exemplary eNB procedure is as follows, and as shown inFIG. 2. The procedure starts in a step S20. Subsequently, a RSRP reportis received in a step S21 from a UE. Based thereon, in a step S22, asubset of a plurality of transmission points is determined forsubsequent use. Then, in a step S23, the eNB allocates interferencecontribution parameters to each resource linked to a transmission pointof the subset. Then, in a step S24, eNB informs the UE of the allocatedinterference contribution parameters α_(i). This can be accomplishedusing RRC signaling or (as a faster option) a PDCCH signaling. The UEuses the signaled interference contribution parameters in obtaining aparameter reflecting channel quality, such as a CQI parameter. This CQIreport obtained based on the allocated/informed α_(i) interferencecontribution parameters is received at the eNB from the UE in a stepS25. Then, the process ends in a step S26 (or is restarted againafterwards based on a trigger).

Thus, as outlined above, the eNB configures the UE with multiplenon-zero-power CSI-RS configurations (interference contributionparameters allocated to linked resources represented by referencesignals RS in a PRB) according to the determined CoMP reporting set. TheCoMP reporting set may be determined for example based on received RSRPreports from the UE. Based on the applied CoMP strategy, the eNBconfigures the UE with the power offsets parameters (interferencecontribution parameters) that the UE assumes in CQI calculation for theinterfering points. The eNB may also additionally configure the UE withthe further power offsets P_c that UE should assume in CQI calculationfor transmitting points or resources carrying payload/useful signals)(or for the overall CQI).

In one embodiment this informing is done via RRC, e.g. when configuringthe UE with the multiple non-zero-power CSI-RS configurations. Inanother embodiment this informing is done via dynamic signaling onPDCCH.

Then, the eNB receives the CSI report from the UE, including CoMP CQI.

A corresponding exemplary UE procedure is as follows, and as shown inFIG. 3. The process starts in a step S30. In a step S31, the UE receivesinterference contribution parameters α_(i) for each resource (e.g.reference signal in a PRB) to which a subset of the plurality oftransmission points is linked. In a step S32, the UE measures thechannel transfer function H_(i) for each channel established by arespective resource (or reference signal), i.e. linked transmissionpoint(s). Also, in a step S33, interference N which originates fromresources not linked to the subset of the plurality of transmissionpoints is measured.

Then, in a step S34, a feedback signal is obtained that is indicative ofchannel quality for each resource linked to the subset and whichresource transmits a “useful”, i.e. payload signal (non-interferingsignal). Similarly, in a step S35, a feedback signal is obtained that isindicative of channel quality for each resource linked to the subset andwhich resource transmits an interfering signal.

In a subsequent step S36, summing (adding) is performed of the derivedfeedback signals scaled with the respective interference contributionparameter and measured interference N.

Then, in a step S37, a reporting signal is selected for being fed backto the another device (i.e. eNB) based on the result of summing and therespective channel quality. That is, such selection can exemplarily beaccomplished based on calculating the ratio of: the sum of obtainedfeedback signals (payload related) and the summed derived feedbacksignal (interference related) plus measured interference N. Thus,calculation is as set out above in relation to calculation of SINR whichis used to obtain the CQI as the reporting signal which is then fed backin step S38 to the eNB. Subsequently, the process ends in step S39 (oris restarted again afterwards based on a trigger such as receipt of anupdate of interference contribution parameters for another CoMPconfiguration).

Thus, as outlined above, the UE receives (S31) from the eNB via higherlayer signaling (RRC) multiple non-zero-power CSI-RS configurations andthe power offset parameter sets: a power offset parameter set that is tobe assumed for interfering points in CQI computation, and a power offsetparameter set that is to be assumed for transmission points transmittinguseful (payload) signal in the CQI computation.

Additionally the UE may receive a RS (which can be zero-power CSI-RS,non-zero power CSI-RS, or other types of RS) configuration e.g. forinterference measurement purposes (which are used to determineinterference of outside the CoMP set).

Alternatively, the UE may receive the power offset parameters(interference contribution parameters) for interfering points as part ofPDCCH signaling, for example within the UL grant that triggers CSIreporting. This allows more dynamic operation of different CoMP schemes(e.g. complete muting versus interference reduction).

UE measures (S32) channel H_(i) corresponding to the multiplenon-zero-power CSI-RS resources, each typically mapped or linked to onetransmission point.

UE measures (S33) interference (parameter N in the above formula forSINR calculation) originating from outside of the CoMP measurement set,e.g. in either of the following ways:

-   -   Measuring the interference power directly from configured RS        resources or other muted RE resources that reflect the        interference outside of the CoMP measurement set, or    -   Subtracting the channel contribution inside the CoMP measurement        set from RS locations and measuring the underlying interference        power. If for example zero-power CSI-RS are used for        interference measurement, with the assumption that zero-power        CSI-RS resources have been configured properly such that exactly        the CoMP measurement set points are muting their transmissions,        the UE will be measuring exactly the correct interference power.

For each CoMP transmission hypothesis, the UE computes (S37) the CoMPCQI as follows:

For each CSI-RS resource (point) transmitting to the UE, UE computes(S34) the relevant feedback (PMI/CQI), and considers the signal as auseful signal in the CQI computation. The useful signal may be scaledwith a transmission point specific scaling factor (power offset P_c,generally distinct from α_(i)) intended to scale useful i.e. payloadsignal.

For each CSI-RS resource (point) within the CoMP reporting (measurement)set transmitting an interfering signal, the UE scales (S35) the channelmeasured from non-zero-power CSI-RS resources with the (potentiallyCSI-RS or transmission point specific) scaling factor (interferencecontribution parameter) and adds it to the measured interference(summing in S36).

In CQI calculation, UE would most likely assume the best PMI for theinterfering points, however the invention does not preclude using anyother PMI as the PMI assumption.

The UE reports the CoMP CQI to the eNB based on the calculation in S38.

Other CoMP systems can benefit also from the principles presented hereinas long as they rely on an identical or similar interferencecontribution parameter allocated to each resource linked to a subset ofthe plurality of transmission points designated for transmission towardsanother device, wherein the interference contribution parameter isindicative of an expected interference contribution originating fromsaid transmission point.

Embodiments of the present invention may be implemented in software,hardware, application logic or a combination of software, hardware andapplication logic. The software, application logic and/or hardwaregenerally resides on control modules or modems. In an exampleembodiment, the application logic, software or an instruction set ismaintained on any one of various conventional computer-readable media.In the context of this document, a “computer-readable medium” may be anymedia or means that can contain, store, communicate, propagate ortransport the instructions for use by or in connection with aninstruction execution system, apparatus, or device, such as a computeror smart phone, or user equipment.

The present invention relates in particular but without limitation tomobile communications, for example to CoMP enabled environments underWCDMA, LTE, WIMAX and or WLAN and can advantageously be implemented inuser equipments or smart phones, or personal computers connectable tosuch networks as well as in network devices such as eNBs. That is, itcan be implemented as/in chipsets to such devices, and/or modemsthereof.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the above-described functions may be optional ormay be combined.

Although various aspects of the invention are set out in the independentclaims, other aspects of the invention comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

It is also noted herein that while the above describes exampleembodiments of the invention, these descriptions should not be viewed ina limiting sense. Rather, there are several variations and modificationswhich may be made without departing from the scope of the presentinvention as defined in the appended claims.

LIST OF EXEMPLARY ACRONYMS USED IN THIS DOCUMENT

CB coordinated beamformingCoMP coordinated multipoint transmissionCS coordinated switchingCSI-RS channel state information reference signalCQI channel quality indicator DL downlinkDPS dynamic point selectionJT joint transmissionPDCCH physical downlink control channelPMI precoding matrix informationRRC radio resource controlRSRP reference signal received power

The present invention proposes methods and devices related tocontrolling UE assumption of interference. To this end, there isproposed a device, comprising a controller module, configured to controla plurality of transmission points, each constituted by a set of atleast one transmit antenna, to transmit data to another device in acoordinated transmission from at least a subset of the plurality oftransmission points, wherein the controller module is configured toallocate, to each resource linked to the subset of the plurality oftransmission points designated for transmission towards the anotherdevice, an interference contribution parameter that is indicative of anexpected interference contribution originating from said transmissionpoint, and to inform said another device of those resources to which thesubset of the plurality of transmission points designated fortransmission towards the another device is linked, together with therespective interference contribution parameter allocated to eachresource. Another device comprises a controller module configured toreport feedback, wherein the feedback signal is based on signals whichare scaled with the respective interference contribution parameterallocated to the respective resource.

1. An electronic device comprising: circuitry configured to receivecoordinated transmission from at least a subset of a plurality oftransmission points, each transmission point comprising at least onetransmit antenna; receive, for each resource to which the subset of theplurality of transmission points is linked, an interference contributionparameter allocated to each resource and indicative of an expectedinterference contribution of the transmission point; and select areporting signal to be transmitted to the another device based on thecoordinated transmission and the interference contribution parameter. 2.The electronic device of claim 1, wherein the circuitry is configured tomeasure a channel transfer function for each channel corresponding to aresource to which the subset of the plurality of transmission pointsdesignated for coordinated transmission is linked.
 3. The electronicdevice of claim 1, wherein the circuitry is configured to measureinterference originating from resources not linked to the subset of theplurality of transmission points.
 4. The electronic device of claim 3,wherein the circuity is configured to obtain a first feedback signalindicative of a first channel quality for each resource linked to thesubset of the plurality of transmission points and transmitting apayload signal.
 5. The electronic device of claim 4, wherein thecircuitry is configured to obtain a second feedback signal indicative ofa second channel quality for each resource linked to the subset of theplurality of transmission points and transmitting an interfering signal.6. The electronic device of claim 5, wherein the circuitry is configuredto sum the first and second feedback signals scaled with a respectiveinterference contribution parameter allocated to a respective resource.7. The electronic device of claim 6, wherein the circuitry is configuredto select the reporting signal based on the result of summing and themeasured interference.
 8. The electronic device of claim 1, wherein theinterference contribution parameters have a value greater than zero andare indicative for a transmission from the transmission point linked tothe resources.
 9. The electronic device of claim 8, wherein a value ofthe interference contribution parameter greater than zero and smallerthan “1” denotes a reduction in interference level, and a value greaterthan “1” denotes an increased interference level.
 10. The electronicdevice of claim 1, wherein the interference contribution parameters havea value equal to zero and denote no transmission from the transmissionpoint linked to the resources.
 11. The electronic device of claim 2,wherein the circuitry is configured to measure interference originatingfrom resources not linked to said subset of the plurality oftransmission points such that interference is measured directly onlyfrom those resources not linked to the subset of the plurality oftransmission points.
 12. The electronic device of claim 11, wherein theresources not linked to the subset are selected for measurement based ontheir configuration to be assumed to be muted due to being attributed atransmission with zero power or a maximum interference reduction. 13.The electronic device of claim 2, wherein the circuitry is configured tomeasure interference originating from resources not linked to the subsetof the plurality of transmission points by measuring the overallinterference and then subtracting the contribution of the resourceslinked to a part of the subset of the plurality of transmission pointsthat are identified as being attributed to transmission with zero poweror a maximum interference reduction.
 14. The electronic device of claim5, wherein the circuitry is configured to select the reporting signal bycalculating the reporting based on a ratio of: a sum of the first andsecond feedback signals, and the sum of the first and second feedbacksignals plus the measured interference.
 15. A mobile station configuredto report feedback to a base station responsive to the base station'scoordinated transmission from at least a subset of a plurality oftransmission points, each transmission point being constituted by a setof at least one transmit antenna, the mobile station comprising:circuitry configured to receive, for each resource to which the subsetof the plurality of transmission points designated for the basestation's coordinated transmission is linked, a respective interferencecontribution parameter allocated to each resource and indicative of anexpected interference contribution originating from the respectivetransmission point; measure interference originating from at least afirst resource not linked to the subset of the plurality of transmissionpoints; obtain a first feedback signal indicative of a first channelquality for each resource linked to the subset of the plurality oftransmission points and transmitting a payload signal; derive a secondfeedback signal indicative of a second channel quality for each resourcelinked to the subset of the plurality of transmission points andtransmitting an interfering signal; sum the first and second feedbacksignals scaled with the respective interference contribution parameterallocated to the respective resource, and the measured interference, andselect a reporting signal to be transmitted to the another device basedon the result of summing.
 16. The mobile station of claim 15, whereinthe respective interference contribution parameters have a value greaterthan zero and are indicative for a transmission from the transmissionpoint linked to the resources.
 17. The mobile station of claim 15,wherein the circuitry is configured to measure interference originatingfrom resources not linked to the subset of the plurality of transmissionpoints such that interference is measured directly only from resourcesnot linked to the subset of the plurality of transmission points.
 18. Amethod of reporting feedback to an apparatus responsive to a coordinatedtransmission from at least a subset of a plurality of transmissionpoints, each transmission point being constituted by a set of at leastone transmit antenna, the method comprising: receiving, for eachresource to which the subset of the plurality of transmission pointsdesignated for the coordinated transmission is linked, a respectiveinterference contribution parameter allocated to each resource andindicative of an expected interference contribution originating from therespective transmission point; obtaining a first feedback signalindicative of a first channel quality for each resource linked to thesubset of the plurality of transmission points and transmitting apayload signal; obtaining a second feedback signal indicative of asecond channel quality for each resource linked to the subset of theplurality of transmission points and transmitting an interfering signal;and selecting a reporting signal to be transmitted based on the obtainedfirst and second feedback signals.
 19. The method of claim 18, furthercomprising: measuring interference originating from at least a firstresource not linked to the subset of the plurality of transmissionpoints.
 20. The method of claim 19, wherein the selecting is based onthe first and second obtained feedback signals and the measuredinterference.